21621478987 has 2 divisors, whose sum is σ = 21621478988. Its totient is φ = 21621478986.

The previous prime is 21621478981. The next prime is 21621479017. The reversal of 21621478987 is 78987412612.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21621478987 - 2²³ = 21613090379 is a prime.

It is not a weakly prime, because it can be changed into another prime (21621478981) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10810739493 + 10810739494.

It is an arithmetic number, because the mean of its divisors is an integer number (10810739494).

Almost surely, 2^21621478987 is an apocalyptic number.

21621478987 is a deficient number, since it is larger than the sum of its proper divisors (1).

21621478987 is an equidigital number, since it uses as much as digits as its factorization.

21621478987 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2709504, while the sum is 55.

The spelling of 21621478987 in words is "twenty-one billion, six hundred twenty-one million, four hundred seventy-eight thousand, nine hundred eighty-seven".